The present invention generally relates to harmonics cancellation, and more specifically, to a method and system for canceling harmonics noise. In general, according to an embodiment, the invention can be applied to attenuating harmonics noise coupled with electronic signals, irrespective of whether the noise arise from known or unknown sources, whether the noise signal is subject to drift, whether the noise is modulated in its amplitude, frequency, and phase, and whether the noise is intermittent or continuous.
A common source of electronic noise in digital systems is the running digital clock. Since there is a running clock in almost every digital system, non-linear effects of such sources can cause clock harmonics (also known as spurs) to be coupled with useful signals. Although electrical isolation methods can suppress such harmonics, they do not guarantee successful operations in all cases. For example, where the input signal may be coupled with harmonics during a signal transmission, a user at the receiving end may not have control over the signal transmission end to create an effective electrical isolation at the source of the noise. Even if the user had control over the signal transmission apparatus, in many cases, due to tight system integration, the harmonics are nevertheless difficult or impossible to isolate.
Another conventional method to suppress clock harmonics is based on detecting harmonics noise during periods where normal useful signals may be absent. One drawback with this type of approach is that not all systems or use cases guarantee there to be periodic windows of time where useful signals are absent. Further, since harmonics noise can be modulated and subject to drift, the determination of the characteristics of the noise during windows when normal useful signals are absent does not necessarily predict the characteristics of the noise during windows when normal useful signals are not absent.
Another conventional method is based on notching out signal energy around the spur frequency. This approach however can introduce unacceptable signal loss in the resulting signals, leading to unacceptable signal-to-noise ratio, for example.
In general, a spur may be located in any baseband frequency, and its frequency, phase, and amplitude can be modulated in unexpected ways. A spur may in general arise from known or unknown sources. A spur may be continuous or intermittent. Harmonics noise in general degrades signal transmission and decreases overall system performance of digital communications systems.